Why would a dog rub itself in a dead animal?

My dog on a walk today found a dead fox and laid his neck in it. We don't know why he would do such a thing, he has never done so before. He is a Shiba Inu, we have raised him from a puppy, and he is now 8 years old.

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One theory I've heard is that dogs rub themselves on dead things to disguise their scent while on the hunt so their prey doesn't know they're there.
Chase loves rolling in dead things. Mammals, birds, fish. If it's dead and rotting she wants to be on it. I think she just likes the smell.
My friend's dog rolls in poop, so it could be worse!